Chronic Fatigue Syndrome (CFS) is a debilitating and poorly understood condition associated with increased healthcare costs and markedly reduced quality of life. To date, treatment approaches for CFS have included pharmacotherapy to address suspected pathogenic factors (e.g., a virus or immune dysfunction) or overt symptoms (e.g. fatigue, mood dysfunction), and nonpharmacological approaches to increase daytime activity or enhance disease-specific coping skills. One of the most universal symptoms of CFS is insomnia (e.g., unrefreshing sleep or sleep onset or maintenance difficulties), but curiously, the benefits of sleep-focused interventions for such individuals remains largely unexplored. This oversight is notable because insomnia results in many of the diurnal symptoms common to CFS. In addition, insomnia adversely affects the same bodily systems (e.g., neuroendocrine and neuroimmune systems) thought to be mechanistically important to this syndrome. Thus, insomnia may be a key etiological factor in CFS, or alternately, insomnia may play a mediational role. We have developed, tested and refined a cognitive-behavioral therapy (CBT) designed to address perpetuating factors in insomnia. Our recent pilot work suggests that CFS patients display some of the perpetuating mechanisms targeted by CBT. Moreover, results from one of our recent clinical cases suggest CBT may be a promising therapy for the insomnia in CFS. In the current project, we will conduct a randomized clinical trial to test the efficacy of CBT as an adjunct to usual medical care among CFS patients who also meet Research Diagnostic Criteria for insomnia. A sample of 50 CFS patients with insomnia will be randomized to usual medical care and adjunctive CBT, or a usual care control condition. Objective (actigraphy) and subjective (sleep log, questionnaire) sleep measures, and measures of fatigue, waking activity, mood, quality of life, and treatment validity will be obtained before therapy, immediately after an 8-week treatment phase, and at a 1-month follow-up. This design allows us to test the efficacy of CBT-I in this group, and explore whether insomnia is mechanistic in driving symptoms in CFS. [unreadable] [unreadable] [unreadable]